The car wasn't porpoising when laterally loaded on Friday, but ultimately excuses about setup and coming on the radio to say the car is "hopping in yaw" (IIRC) are just excuses. Russell's teammate just plain outperformed him and did a better job. Likewise as when Russell outperformed the other Mercedes when Hamilton went the wrong way with setup in Jeddah.
Who knows what Mercedes did (or didn't do in response to track evolution) to make the car perform worse, but they clearly did!